JPH0825086B2 - Processing method using ball end mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a linear cutting edge in which a rotation locus around the rotation axis of the main body is a substantially flat surface perpendicular to the rotation axis at the tip of the main body The present invention relates to a method capable of processing the surface of a work material with high accuracy by using a ball end mill equipped with the above and significantly shortening the time required for finishing work.

<Prior Art> A ball end mill is known as one of tools for processing a three-dimensional curved surface of a press die or the like via a numerical control device or a copying device.

This ball end mill has one or more arc-shaped cutting edges on the tip side of a cylindrical main body whose rotation locus around the rotation axis of this main body is almost spherical. As shown in FIG. 7, it is attached to a spindle 11 of a machine tool such as a machining center or a die machining machine having at least three orthogonal control axes.

The ball end mill 12 shown in FIG. 7 is a two-flute type having two arc-shaped cutting edges 13 and 14.
It is adapted to rotate together with the main shaft 11. And
For example, in the drawing, a Z-direction incision and a Y-direction feed are repeatedly applied to the ball end mill 12 for the work material 15, and the surface of the work material 15 (hereinafter, referred to as a work surface).
Is designed to be processed. That is, the ball end mill 12 is driven and rotated to be fed in the Y direction, whereby the arcuate cutting edges 13 and 14 scrape off the work surface into a groove shape. Next, the ball end mill 12 is moved in the X direction by a certain amount p, and then is sent in the Y direction again to scrape the surface to be cut into a groove shape. At this time, the work surface can be machined into a three-dimensional curved surface by changing the Z-direction cut at the same time as the Y-direction feed of the ball end mill 12.

The movement amount p of the ball end mill 12 in the X direction, which is the repetitive interval in the Y direction, is called the pick amount.

By the way, when the ball end mill 12 having the arcuate cutting edges 13 and 14 as described above is used for the cutting work, a line having a height h called a cusp is called on the work surface along with the repeated feeding in the Y direction. Since the trace 16 and the conical uncut portion 17 which is generated each time the ball end mill 12 makes one rotation in association with the feed in the Y direction are inevitably generated, the streak 16 and the uncut portion 17 are handgrinded in a later step. It is necessary to work to remove it.

Therefore, in order to reduce the scratches 16 formed on the surface to be cut, in the ball end mill having one or more arc-shaped cutting edges whose rotation loci around the rotation axis are substantially spherical, the arc-shaped cutting edges It has been proposed that a straight cutting edge is formed on the leading end side in a continuous manner with the arcuate cutting edge and the rotation locus around the rotation axis of the main body is a substantially flat surface perpendicular to the rotation axis. .

<Problems to be Solved by the Invention> A ball end mill having a linear cutting edge connected to the arcuate cutting edge on the tip side of the arcuate cutting edge has an effect of reducing streaks 16 shown in FIG. However, it is not possible to reduce the conical uncut portion 17 that is generated each time the ball end mill 12 makes one rotation with the feed in the Y direction.

As a result, the above-mentioned uncut portion 17 becomes a sharp projection and remains on the surface to be cut, and a great amount of time is required for the hand-finishing work by the grinder in the subsequent step.

Here, the mechanism of generation of the uncut portion 17 will be described by taking a two-blade ball end mill constituted only by arcuate cutting edges without linear cutting edges as an example.

It should be noted that the mechanism of uncut residue is the same even when the number of blades is three or more, but the uncut residue decreases as the number of blades increases.

The rotation axis of the main body, which rotates 6000 rpm, feeds sequentially from point O ₁ to point O ₈ at a feed rate of 6000 mm, and the movement loci of arc-shaped cutting edges 13 and 14 projected on the work surface 8
Shown in the figure. However, the one arc-shaped cutting edge 13 shown by the thick one-dot chain line shows only the portion where the work material is actually cut, and the other arc-shaped cutting edge 14 similarly shown by the thick two-dot chain line.
Also, although only the part where the work material is actually cut is shown, each has a length longer than this.

Here, focusing on an arbitrary point Q on the left work surface in the figure, which is a downcut with reference to the movement trajectory of the rotation axis of the ball end mill, this point Q is the rotation axis of the ball end mill. _Although it is cut by one arcuate cutting edge 13 at the position of ₁ , the large uncut portion on the left side in the figure based on the movement trajectory of the rotation axis of the ball end mill causes the ball end mill to rotate counterclockwise. This is the case, and in the case of reverse rotation in the clockwise direction, the uncut residue occurs on the right side in the figure with reference to the movement trajectory of the rotation axis of the ball end mill. Then, when the rotational axis moves to the position of the point O ₂ , it is ground by the other arcuate cutting edge 14. Line segment O ₁ Q
And the line segment O ₂ Q form part of the arcuate cutting edges 13 and 14, these line segments O ₁ Q and O ₂ Q are located at the lowest point of the points O ₁ and O ₂ (cutting point). The point Q is a circular arc which is the maximum cutting depth with respect to the material, and the point Q is a position higher than the points O ₁ and O ₂ , that is, the uncut portion having a convex cone shape.

For example, using a ball end mill with a diameter of 10 mm under the above conditions and a change in the work surface with the progress of machining when the pick amount is 0.6 mm, as shown in FIG. On the left side in the feed direction, a conical uncut portion 17 having a height of 25 μm occurs.

However, the uncut portion 17 is generated only on the work material 15 having a work surface that is substantially perpendicular to the rotation axis of the ball end mill 12, but it is generally shown in FIG. Since it is higher than the height h of the mark 16 and significantly reduces the surface roughness of the surface to be machined, it poses a serious problem on the accuracy of the machined surface.

In addition, since the rotation loci of the arc-shaped cutting edges 13 and 14 are spherical, a slight uncut portion is generated even on the right side in the feed direction, which is the up-cut based on the ball end mill 12, but the left side described above. Compared to, it is not so much as a problem.

<Object of the Invention> The present invention reduces the conical uncut residue that occurs with each revolution of the ball end mill along with the feed movement with respect to the work material, thereby improving the accuracy of the surface roughness of the work surface,
It is an object of the present invention to provide a processing method using a ball end mill that can significantly reduce the time required for finishing the work surface.

<Means for Solving the Problem> The processing method using the ball end mill according to the present invention is
An arc-shaped cutting edge whose rotation locus around the rotation axis of the main body is substantially spherical, and a circle formed around the rotation axis of the main body that is formed on the tip side of the arc-shaped cutting edge and is continuous with the arc-shaped cutting edge. A ball end mill having a linear cutting edge whose rotation locus is substantially flat and perpendicular to the axis of rotation is used, and a relative feed is repeatedly applied to the work material to give the work material. In processing the surface of the ball end mill, the feed rate of the ball end mill and the feed rate of the ball end mill are reduced so that the uncut uncut residue generated for each rotation of the ball end mill with the feed movement of the ball end mill with respect to the work material is reduced. It is characterized in that the feeding repeat interval and the rotation speed of the ball end mill are set.

<Operation> The conical uncut residue that occurs each time the ball end mill makes one revolution due to the feed to the work material is inevitably caused by the arcuate cutting edge as described above. Is.

Therefore, in order to eliminate this uncut residue, at least the tip side of the cutting edge must be linear. In other words, regarding the shape of the ball end mill itself, a linear cutting edge whose rotation locus around the rotation axis of the main body is a substantially flat surface perpendicular to the rotation axis is placed closer to the tip than the arc cutting edge. It is necessary to form them in series, and it is necessary to have a shape similar to that of the ball end mill already proposed.

Here, as it is apparent from FIG. 7 that only the width region corresponding to the pick amount p is finally left as the machining end surface, the linear cutting is performed so that only the width region is left uncut. Just decide the length of the blade.

However, the longer this linear cutting edge, the more the shape becomes different from that of a normal ball end mill, which makes NC machining programming difficult and other practical problems become apparent. Therefore, it is preferable to keep the length of the linear cutting edge to the minimum necessary.

Based on the above knowledge, the straight line projected on the work surface when the rotational axis of the main body of the two-blade ball end mill with linear cutting edges is fed sequentially from point O ₁ to O ₈ at a speed of 6000 mm per minute Fig. 1 shows the locus of movement of the shaped cutting edge.
However, for the one straight cutting edge 18 shown by the thick dashed line,
An arc-shaped cutting edge (not shown) is formed continuously to this, and similarly to the other linear cutting edge 19 indicated by a thick two-dot chain line, an arc-shaped cutting edge (not shown) is also formed continuously to this. There is.

In such a state, in order to eliminate the uncut portion of the area corresponding to half of the pick amount p finally left as the processed surface,
All of this area may be cut by the straight cutting edges 18 and 19. For example, assuming that the lengths of the linear cutting edges 18 and 19 are as shown in FIG. 1, the shaded areas g ₁ and g _{2 in} the figure are not cut by the linear cutting edges 18 and 19. Since it is cut by an arcuate cutting edge (not shown) continuous with the linear cutting edges 18 and 19, a conical uncut portion is left.
Therefore, the minimum length of the linear cutting edges 18 and 19 that completely scrapes off the remaining portion as the machined surface is the condition that both the regions g ₁ and g ₂ disappear in FIG. ₁ , that is, M ₁ = M ₂ and N ₁ = N ₂
Is the larger value of the lengths γ of the linear cutting edges.

In addition, M ₁ and M ₂ are the moving path of the rotation axis and the linear cutting edge 1
The intersections with the loci of outermost positions of 8,19, N ₁ and N ₂ are line segments 1 and linear cutting edges parallel to the locus of movement of the rotation axis and separated by p / 2 from the movement locus of this rotation axis. It is the intersection with the locus of the outermost position of 18,19.

Here, the number of blades of the ball end mill is Z, the feed rate is F (mm) per minute, the number of revolutions is N (rpm) per minute, and the ball end mill from point O ₃ to point O ₉ where M ₁ = M ₂ The time I moved
when the t _M, the length gamma _M linear cutting edge as the M ₁ = M ₂ is
Under the conditions of the following formulas (1) and (2) Should be satisfied.

Therefore, in order to eliminate the uncut uncut portion in the region g ₁ of the work surface shown in FIG. 1 described above, the above (1),
It is necessary to satisfy the following expression (3) under the condition of (2).

On the other hand, the length γ _N of the linear cutting edge with N ₁ = N ₂ is The area of the work surface shown in FIG. 1 described above is given by
In order to eliminate the uncut uncut portion in g _2, the condition of the following expression (4) must be satisfied.

Then, the larger one of the lengths γ _M and γ _N of the linear cutting edges calculated from the expressions (3) and (4) is the minimum length of the intended linear cutting edge. In other words,
Based on the lengths of the linear cutting edges 18 and 19 formed on the ball end mill, the pick amount p, the feed speed F or the rotation speed N without any uncut uncut portion can be appropriately set.

By the way, in the conventional invention aiming to eliminate only the known streak, the length of the linear cutting edge is half the interval of the streak, that is, p / 2, the streak completely disappears, so It is meaningless if the length of the cutting edge is p / 2 or more. On the other hand, in order to eliminate the uncut uncut portion that is the subject of the present application, the length of the linear cutting edge needs to be at least p / 2, but the length of the linear cutting edge is p / 2. In this case, it is necessary to set the number of rotations of the ball end mill to a very high value with respect to the feed speed.

<Example> As shown in FIG. 2 showing the appearance of a ball end mill in which the present invention can be carried out, two linear cutting edges 22 and 23 arranged so as to cross the rotation axis 21 of the main body 20 and these linear cutting edges. Cutting edge 22,
Using a ball end mill 26 with a diameter of 20 mm having two arc-shaped cutting edges 24, 25 continuous to 23, it is necessary to eliminate uncut residue under the condition that the pick amount is 0.6 mm at 6000 rpm. The relationship between the length γ of the linear cutting edges 22 and 23 and the feed speed F is shown in FIG. As is clear from FIG. 3, it is necessary to increase the length γ of the linear cutting edges 22 and 23 as the feeding speed F becomes higher. For example, the feeding speed F of 12000 mm / min.
In the case of, the length γ of the straight cutting edges 22 and 23 is 1.0
It must be at least mm (1.67 times the pick amount).

As shown in FIG. 3 which shows the measured value of the surface roughness of the surface to be cut when cutting with this ball end mill, the surface roughness of the surface to be cut was approximately 1.0 μm in terms of R _max , which was almost flat.

Comparing the surface roughness of the work surfaces using the conventional ball end mill shown in Fig. 7 under the same cutting conditions, the surface roughness of the conventional ball end mill was R _max .
It was also confirmed that it was worse than 30 μm.

In the present invention, the surface to be cut can be geometrically made into a completely flat surface, but the actual cutting results show that the surface to be cut is not a completely flat surface, as is apparent from FIG. Absent. The reason for this is that the cutting edge of the linear cutting edge is not completely flat and sharp, and the work piece is slightly welded to the cutting edge, so that the work surface is roughened.

Next, using the same ball end mill as in the above-mentioned embodiment, the feed rate is 6000 mm / min and the pick amount is 0.6 mm.The linear cutting edge length γ and its necessary to eliminate uncut residue under the condition of 0.6 mm. The relationship with the rotation speed N is shown in FIG. As the rotation speed of the ball end mill increases, the length of the linear cutting edge γ
It turns out that is shortened.

As is clear from FIG. 5, the higher the rotational speed of the ball end mill, the closer the length γ of the linear cutting edge becomes to half the pick amount p, which is 0.3 mm.

FIG. 6 shows measured values of the surface roughness of the work surface when cutting with this ball end mill. In this case, the surface roughness of the work surface is about 1.0 μm in terms of R _max, which is almost flat, but with the conventional ball end mill, the best surface roughness can be obtained at 24,000 rpm, but the value is R It was also found that the _maximum display was worse than 12 μm.

<Effects of the Invention> According to the processing method using the ball end mill of the present invention, the feed speed and rotation speed of the ball end mill, the length and number of linear cutting edges formed on the ball end mill, and the ball end mill. Since the feed repeat interval is set to the optimum value, there is no uncut uncut residue that is the biggest cause of deterioration of the surface roughness of the work material, and the surface roughness of this work material can be greatly improved. You can As a result, the surface of the work material is ground to be substantially flat, and the time required for the finishing process after processing can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a working principle diagram of the present invention showing a moving locus of a linear cutting edge formed on a ball end mill, and FIG. 2 is a front view showing an appearance of an embodiment of a ball end mill capable of carrying out the present invention. FIG. 3 is a graph showing the relationship between the feed rate of the ball end mill according to the present invention and the length of the linear cutting edge, FIG. 4 is a graph showing the distribution of the surface roughness thereof, and FIG. 5 is the rotation of the ball end mill according to the present invention. 6 is a graph showing the distribution of the surface roughness, FIG. 7 is a processing conceptual diagram showing the conventional cutting situation, and FIG. 8 is its processing. Principle diagram, FIG. 9 is a processing conceptual diagram for explaining the principle of uncut portion. In the figure, reference numerals 12 and 26 are ball end mills and 13, 24 and 25
Is an arcuate cutting edge, 15 is a work material, 16 is a streak, 17 is a conical uncut portion, 18, 19, 22, 23 are straight cutting edges, 20 is a main body, 21 is a rotation axis, and γ is The length of one linear cutting edge, p is the pick amount.

Front page continued (72) Inventor Fumio Inouchi, 1 Uzumasa Tatsumi-cho, Ukyo-ku, Kyoto Prefecture Mitsubishi Heavy Industries, Ltd. Kyoto Seiki Co., Ltd. Kyoto Seiki Works

Claims (1)

[Claims] 1. An arc-shaped cutting edge whose rotation locus around the axis of rotation of the main body is a substantially spherical strip, and a main body of the main body which is formed on the tip side of the arc-shaped cutting edge and is continuous with the arc-shaped cutting edge. Using a ball end mill equipped with a linear cutting edge whose rotation locus around the axis of rotation is substantially planar and perpendicular to the axis of rotation, the ball end mill is repeatedly fed relative to the work material. When processing the surface of the work material, the ball end mill is reduced so that a conical uncut portion that occurs with each rotation of the ball end mill with the feed movement of the ball end mill with respect to the work material is reduced. The method for processing using a ball end mill is characterized in that the feed rate of the above, the repeating interval of the above feed, and the number of revolutions of the above ball end mill are set.